Method of expanding pistons



Feb. 25, 1936. E. A. KOETHER METHOD OF EXPANDING PISTONS Filed Nov. 14, 1934 II I 71/41/4141 Patented Feb. 25, 1936 UNITED STATES PATENT OFFICE METHOD OF EXPANDING PISTONS Maryland Application November 14, 1934, Serial No. 753,025

14 Claims.

This invention pertains to an improved method of and apparatus for expanding pistons.

' The invention is primarily applicable to the expansion of skirts of pistons of the split skirt type which have collapsed in use, the method being such that the skirt may be evenly and quickly brought to size in order to insure proper fit with the wall of its companion cylinder. In fact, the method is such that the amount of expansion may be controlled with the highest degree of accuracy and can, moreover, be utilized to expand the piston at the lower end more than at the upper end, and vice versa, when necessary. It is, likewise, possible to expand the piston into an oval shape.

Stated in a broad sense, the method consists in projecting through the action of a blast, a plurality of bodies or particles simultaneously and directly against and over a substantial area of the inner face of the piston or the skirt there of. In other words, the process involves the bombardment of the inner face of the piston or any predetermined area. thereof with a mass of particles which act to equally expand the body, and at the same time, tend to remove any burned oil or the like which may be present if the piston which is undergoing treatment or expansion is a used one.

It has heretofore been proposed to enlarge the diameter of a relatively small piston by percussion; this is evidenced by U. S. Letters Patent to McCormack and Searle, No. 1,181,467, dated May 2, 1916, wherein the point of a hammer 41 is caused to deliver a blow upon the inner surface of the piston through the action of a spring 48, the piston being turned step-by-step with reference to the hammer.

Insofar as I am aware, this method has never been employed, and it is probably due to the fact that the peening action of the hammer is 10- calized at a series of points extending circumferentially around the inner face of the piston. Moreover, the action of the hammer is dependent upon a spring, the force of which will gradually decrease during its life or, in other words, is not constant, and in the showing made in the patent referred to, no means is provided for adjusting the tension of the spring and, consequently, the force of the blow or impact of the hammer 41.

While the patent proposes through the peening action to enlarge the diameter uniformly, the.

operation at best is slow, if in fact any such uniform result may be had. Localizing the impact through the peening hammer tends to cause the metal to flow and this is not overcome by producing another blow immediately adjacent thereto, as the metal will tend to flow into the theretofore formed or produced pit or opening.

In the present case, there is no localization of a blow but, on the other hand, a multiplicity of 5 blows is imparted over a substantial area and over the desired area simultaneously, with the result that any displacement of the metal of the piston is substantially uniform.

In the annexed drawing, several embodiments 10 of apparatus are shown, whereby the inner surface of the skirt of the piston may be subjected to a bombardment of bodies or particles propelled and thrown against the skirt through the action of an air blast or other medium.

In the drawing,

Fig. 1 is a vertical sectional view, with parts in elevation, showing a piston mounted upon a stand in position to be subjected to the bombard- 20 mg action;

Fig. 2, a perspective view of an adjustable encircling sleeve placed about the'piston to prevent the particles or bodies employed to bombard the piston from passing outwardly through the openings commonly found in a piston;

Fig. 3, a view similar to Fig. 1, illustrating means for closing off the inner ends of the piston pin bosses and also for localizing the blast against the diametrically disposed portions of the skirt;

Fig. 4, a perspective view of one of the guards employed in the arrangement shown in Fig. 3;

Fig. 5, a side elevation of a modified form of blast nozzle which may be utilized;

Fig. 6, a face view thereof seen at right angles to that shown in Fig. 5; and

Fig. 7, a sectional elevation of a further form of nozzle.

Referring first to Fig. 1, l0 denotes the base quired to make the skirt conform to a cylinder is, of course, relatively small.

A piston to be expanded is shown as seated upon one of these shouldered portions and is 55 gaseous or fluid 15 These hearings or stepped It will be appreciated that the degree of expansion redesignated generally in said figure, by I3. The piston pin bosses'are shown as filled by plugs I4 of any suitable material, such, for instance, as steel, wood or cork, and surrounding the outside of the piston and covering the openings which extend through the walls thereof is a shield or sleeve IS. The ends of the sleeve overlap and the outer section is provided with a slot l6 through which extends a threaded stem ll secured at its inner end to the inner overlapping portion of the member l5 and carrying a wing nut l8 by which arrangement the sleeve may be held closely to the outside of the piston when once adjusted with reference thereto.

To hold the lower end of the piston in close contact with the stepped portion or element I2 upon which it is brought to rest, a bail l|9 pivoted upon pins 2| carried by the base I0 is employed. The bail at its cross portion carries a threaded stem 22 having a knurled head 23, the stem at its lower end bearing upon the upper face of a plate or washer-like element 24 resting upon the upper end of the piston and exerting an endwise thrust thereon as the stem or screw is turned inwardly. The piston is thus maintained in position upon the stand, and through the utilization of the plugs l4 and the encircling band or shield IS, the passage of any particles to the bearing surfaces of the piston pin bosses or to the outside of the piston is prevented.

The bombarding material is, as above indicated, designed to be forcibly thrown against the interior surface of the piston, or more specifically the piston skirt, either in whole or in part. Such material or substance may be shot, crushed steel shot, or any material or substance having suflicient body to efiect the desired action.

The material may be introduced through a nozzle and impelled therefrom through the action of fluid under pressure. As will be seen upon reference to Fig. 1, the base I0 is provided with a central opening through which there extends a pipe 25 surmounted by a nozzle 26 which, as shown in said figure, is open at opposite sides with a centrally disposed downwardly projecting deflector 21, which acts to guide the particles laterally through the oppositely disposed openings in the nozzle.

Pipe 25 is connected with any suitable source of fluid pressure, which pressure will depend upon the character of the material of which the piston is formed and also the nature of the impacting or bombarding material carried forward and projected by the fluid stream. Air under pressure varying anywhere from 40 to pounds has been successfully employed, though higher or lower pressures may be utilized, depending upon the factors of time, piston material, character of bombarding or impacting material, and extent of expansion necessary or desired.

It may be desired to project the disconnected impacting particles or bodies against all portions of the skirt, and to this end the pipe 25 may be moved longitudinally and likewise rotated about its axis. With a view of rotating the same, a reciprocating rack as 28, cooperating with a pinion 29 secured to the pipe 25, may be employed. Motion may be imparted to the rack by any suitable means. Any suitable mechanism for moving the pipe endwise and rotating the same about its axis may, of course, be utilized.

In carrying out the method, the expansion of the piston takes place very quickly but in order to draw off any impacting material, pipes or conduits 3| and 32 may open into the lower portion of the stand Ill and lead off to the supply from which the shot or other impacting material is withdrawn for projection through the nozzle 26.

In actual practice, it has been found that a piston of 3% diameter taken from a Ford machine, was expanded .011" in 40 seconds, with a blast of crushed shot at 90 pounds pressure. A strut type piston of 3%" diameter was likewise expanded in 40 seconds to .006" with similar material and like pressure. These are given merely by way of example.

It will thus be seen that the action is almost momentary, and, in addition thereto, it is found to be uniform throughout the extent of impaction; in other words, there is no undue stretching of the metal at any one point over another.

By the utilization of the plugs I4 and the surrounding sleeve or shield l5, all contact surfaces of the piston are protected. The piston may be readily removed and the protecting elements as readily withdrawn, with a view of putting another piston in place with reference to the nozzle.

In Fig. 3, a slight modification is shown. In this instance, instead of using plugs as I4, guard plates of substantially L-shaped form are employed. The upright body portion of these plates is designated by 33 and from and at the upper end there extends at right angles a section 34. The base or lower end of the member 33 is turned outwardly to a slight extent and a slotted finger as 35 projects therefrom.

A pair of such guard plates is shown in position within the piston in Fig. 3, the upper ends overlapping and the lower slotted ends being attached to the base plate Ill by set screws 36. The upright portions 33 are of such extent as to entirely close off the piston pin bosses 31 and 38. By reason of the fact that the plates are adjustable toward and from each other, the structure may be adapted to pistons wherein the inner ends of the piston pin bosses are nearer to or further apart than the last one positioned upon the base l0.

A surrounding shield or band I5 is also shown positioned about the piston in this figure.

Various forms of nozzles may be employed, and in Figs. 5 and 6 a nozzle having two oppositely disposed mouths 39 and 40, relatively narrow in cross section as compared to their height, is shown. The center of the upper portion of the nozzle, in line with the connection for the pipe or conduit to which the nozzle is attached, is depressed as at 4|, so as to cause an equal deflection of the impacting material laterally and out through the mouths to the opposite sides of such deflector.

In Fig. 7, a further form of nozzle is shown wherein the body of the nozzle which is to be attached to the conduit is denoted by 42, and an adjustable baffle or deflector 43 is mounted above the upper open end thereof. The upper edge of the member 42 is preferably formed parallel with the under face of the cone-shaped baflle 43, to produce an even flow of the impacting material around the entire extent or mouth of the nozzle without any undue impedance.

The simple forms of nozzle are, however, preferred, and the same effect that is accomplished by the outflow of the material entirely around the upper end of the nozzle 42 and beneath the deflector 43 may be had by rotating the conduit as 25 with a nozzle having one or more openings therein.

In the arrangement shown in Fig. 1, and the parts in the position as depicted therein, and with the understanding that the conduit 25 is held stationary, the blast or stream of impacting material is directed only on a diameter at right angles to the axis of the piston pin bosses, as will readily be appreciated.

Under this arrangement, assuming that the bombarding or expanding material has been forced outwardly under proper pressure and for the proper time interval through the nozzle, the piston is expanded only on this diameter and the result is the same as a cam ground piston.

The fact that the method may be employed either with a plain piston, a piston of the strut type, or to produce an expansion comparable to cam grinding. shows the adaptability of the method.

The method may also be advantageously employed to reclaim pistons that have been ground or turned undersize as the skirt of the piston is free, diametrically considered, of any mechanical restraint or holding action, and the metal therein may be so worked as to expand the body of the skirt to increase the outside diameter thereof.

Pressure of the fluid medium, hardness of the impacting material carried thereby, time of impaction of such material against the inner face of the piston, and the character of the material of which the piston is formed, are, of course, the factors which have to be taken into consideration. It has been found that #10 steel shot produced the desired effect and, likewise, gave a much smoother appearance to the inside of the piston than where the shot is broken up or impacting material having a broken surface presenting angles is employed; these latter have a tendency to cut.

The projection of a stream or streams of freely movable, disconnected bodies against the inner surface of a piston impacts or compresses the metal uniformly at those parts against which the stream is directed. Hence, a new piston may be treated by the present method and have the metal on the inside of the skirt worked to such an extent as to cause an outward expansion of the skirt, be the skirt thereof continuous or cut.

With an old piston, bodily expansion of the skirt is effected by working the metal therein as a result of the blast of impacting particles, which compresses the metal on the inside of the skirt and serves to lengthen the effective life of such treated piston by reason of the expansive action of the skirt as wear thereof takes place in use. Thus, a piston which has become worn may be re-sized and the metal on the inside worked to such an extentas to compensate for further wear over a considerable period of time, since the inside of the piston is not aifected by wear on the outside and the compressed metal on the inner surface will tend to cause an outward movement of the piston skirt.

Where a new uncut piston with its outer surface unrestrained is treated and consequently expanded, it will, moreover, spring outwardly when the usual cut is made in the skirt thereof, and the outer surface of the skirt while expansion thereof is being effected, is free of any mechanical restraint or holding action. As above noted, by varying the time interval and the pres sure employed in the blast, the degree of expansion may be regulated to a nicety.

It is manifest that insofar as the method is concerned, it may be practised in connection with apparatus other than that disclosed herein, and the invention is not to be limited thereto.

No claim is made herein to the apparatus set forth in the foregoing specification and as shown in the drawing, inasmuch as the same forms the subject matter of my divisional application, Serial No. 17,545, filed April 20, 1935; the division having been made pursuant to the requirements of the Patent Oflice.

. What is claimed is:

1. That method of expanding the skirt of a piston which consists in projecting a stream of hard bodies against the inner surface of the piston over an area materially in excess of the area of contact of one of said bodies separately considered, the outer surface of the skirt being free of mechanical restraint during such operation, whereby the metal of the skirt is so worked as to definitely expand the same and thereby increase the outer circumference of the skirt.

2. That method of physically expanding the skirt of a piston independently of any inherent spring action therein which consists in subjecting the inner face thereof in part at least, to a bombardment of separate particles or bodies.

3. That method of increasing the outer diameter of a certain portion of the skirt of a piston which consists in subjecting the inner surface of that portion of the piston that is to be expanded to the impact of relatively small bodies thrown thereagainst by fluid pressure, the skirt being free of mechanical restraint during such action.

4. That method of expanding a definite section of the skirt of a piston, which consists in subjecting the inner surface of said section to a blast of small particles under pressure, and for a time interval sufficient to bring about the re uisite expansion of such section.

5. That method of expanding the skirt of a piston which consists in simultaneously projecting a plurality of loose bodies against the inner surface thereof, the outer surface thereof being free of mechanical restraint during such treatment.

6. That method of expanding the collapsed skirt of a piston which consists in projecting a stream of solid particles in a predetermined direction against the inner surface thereof.

7. That method of expanding the skirt of a piston to produce an exterior surface comparable to a cam ground one which consists in projecting a stream of solid particles against the inner surface of the piston at substantially right angles to the axis of the piston pin bosses of the piston.

8. That method as set forth in claim 7, wherein two oppositely disposed streams are projected at substantially right angles and to each side of the axis of the piston pin bosses of the piston.

9. That method of expanding a portion of the skirt of a piston which consists in projecting a stream of shot against the inner surface of only that portion thereof that is to be enlarged.

10. That method of increasing the external diameter of a piston skirt which consists in expanding the same by compressing the metal uniformly on a portion only of the inner surface of the skirt by impact of particles projected thereagainst.

11. That method of expanding the split skirt of a piston to produce an exterior surface com- J parable to a cam ground one, which consists-in projecting a stream of solid particles against the inner surface of the'piston at substantially right angles to the axes of the piston pin bosses of the piston. v I a 12. That method of expanding the skirt of a piston of the split skirt type, which. consists in projecting a stream, of shot against the inner surface thereof, whereby the metal of the skirt is so worked as to bodily expand or increase the outer diameter of the skirt.

13. That method of expanding the skirt of a piston having piston pin bosses formed as an integral part thereof, which consists in closing said bosses against entrance'of any material vthercto,protecting theputer surface oi!v the pisticles or bodies, whereby the external diameter 7 I 01' the skirt will be increased.

14. That method of expanding the skirt of a piston which consists in directing a blast of hard separate particles against the inner face of the skirt in'part at least, andcontinuing such operation until the desired expansion has been efl'ected.

EMIL A. KOE'I'HER. 

